As already disclosed in the aforementioned co-pending patent application, it is known to melt a glass batch continuously in a vertically oriented melting chamber formed of conventional refractory material using various type electrode arrangements supplied with alternating current. It is also known to locate one set of heating electrodes at the upper level of the molten glass zone and to further include at least one setof electrodes located therebelow in the molten glass having separate control means for applying electrical energy to each set of electrodes. As also already known, the method and apparatus described in said co-pending application ameliorates problems encountered when the raw batch material cannot be continously and uniformly melted in said chamber to provide reliable degasification of the molten glass in a manner imparting improved thermal efficiency for the glass melting process.
In one earlier known power control system for continuous glass melting entirely by electrical energy in this general type vertically oriented melting furnace there is employed two sets of electrodes disposed in the upper level of the melting chamber with the lower region of said melting chamber being devoid of electrode heating means so that the molten glass can be completely refined in said lower region of the melting chamber by radiant heat penetrating from the upper zone with a minimum of turbulent glass circulation. The molten glass temperature is said to be maintained greatest intermediate said electrode levels and dissimilar electrode configurations are utilized at each of said levels in order to further obtain a particular thermal circulation path in the molten glass said to be desirable. In a different power control system reported to be useful for electrically melted glass in this same general manner, there is disclosed three electrode levels aligned vertically in the melting chamber and which employ a set of six electrodes with pairs of said electrodes being connected to each phase of a three-phase alternating current power supply. The rate of electrical power being supplied to each level of electrodes in the melting chamber is controlled set of the rate being greatest at the top level electrodes and decreasing successively at each level therebelow which is said to be desirable in order to refine the molten glass at the lowest level in the melting chamber before being withdrawn therefrom. In a more recently reported power control system for melting glass in the same general manner, there is disclosed control means wherein a set of electrodes disposed at the mid-level in the melting chamber is operatively associated with a second set of electrodes disposed at the top level of the melting chamber so as to vary the electrical power distribution therebetween in various ways. The individual power control means for each electrode level cooperate to exercise power ratio control which can be constant or variable and further temperature control means are associated with the control loop for the lower level electrodes to exercise limited authority in this control system. The temperature control being exercised in the melting chamber is said to permit refining of the molten glass in the lowermost region of a vertically oriented type furnace construction.